For measurement technique, analytics, data storage, image storage and image processing, as well as generally for optical tele and data communication, optoelectronic components, in particular formed as optical filters, are frequently necessary, which can be tuned to several adjacent wavelengths. Filters of this kind, for example, consist of what is referred to as Fabry Perot filters, which have at least two DBR minors separated by a cavity (DBR=Distributed Bragg Reflector). Such filters are reflective in a wavelength range identified as a stopband, preset by their construction, however in a thin passband (=Dip) situated inside this stopband they are transmitting. The DBR mirrors for this purpose each contain at least one layer period that consists of two or more layers with different thicknesses and/or refractive indices. The number of layer periods is mostly integral, however, it can also be half-integral, e.g. if at the end of a stack formed by layer periods not all the layers of the respective period come to lie. By the number of layer periods and the refractive index contrast, the width of the stopband and the reflectivity profile in the stopband, and, by the optical length of the cavity, the location of the transmission band or the location of its central or dominant wavelength can be selected or determined. Finally, in Fabry Perot filters, it is possible to change the dominant wavelength of the transmission band within the tuning range preset by the stopband by changing the geometric and with it also the optical length of the cavity by shifting the two DBR mirrors in relation to each other. The component in this way can be tuned to one of several wavelengths 11,12 . . . 1n.
Optical components of the kind have been described in, for example, DE 103 18 767 A1. Their application results in the disadvantage that tuning the filter in the entire stopband is mostly not possible for constructive reasons, or it is associated with high technical effort. For avoiding this disadvantage, several filters with different electronic tuning ranges could be provided, but this would also be expensive. Apart from that, it is frequently undesirable to tune the filter by relatively shifting the DBR mirrors, in particular if it is to serve the purpose of determining or establishing the intensity at a defined wavelength in a radiation irradiated by a radiation source (e.g. light), with which wavelength of a multitude of possible wavelengths the radiation is currently irradiated by the radiation source.
An aspect of the present invention is to provide an optical filter of the type described above, which can be produced inexpensively and with which a multitude of wavelengths can be detected, wherein, however, tuning by shifting the DBR mirrors is not necessary. An additional aspect of the present invention is to provide a process for the production of such a filter. A further aspect of the present invention is the use of the apparatus.
In an embodiment, the present invention an optical filter array which includes a substrate permeable to an electromagnetic radiation to be detected, a first DBR mirror arranged on the substrate, a second DBR minor arranged above the first DBR mirror, and a plurality of cavity sections. The cavity sections have different respective optical lengths, and are arranged so as to be spatially separated from each other between the first DBR minor and the second DBR minor. Each of the first DBR mirror, the second DBR mirror, and the plurality of cavity sections with different optical lengths form filter elements of a filter. The filter reflects in a stopband determined by the first DBR minor and the second DBR minor. Each filter element has at least one narrow transmission band determined by the optical length of its respective cavity section located inside the stopband. A different thicknesses of the cavity sections is provided via a nanoimprint process.